Ana and TD 3 take aim at the Lesser Antilles

Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.

Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.

Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD

Tropical Depression Three forms, could be Bill later todayQuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.

Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.

Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.

I do agree with you but models are in good agreement with BILL going north of PR! With sunch good agreement it's hard not to believe it BUT these models are really over doing BILL with the intensity forecast and hence they are futher north!I don't see BILL rapidly intensifying - YUP I am going against what NHC is saying...not the first time!! HAHA!

Quoting atmoaggie:Y'all know what is more annoying than WS's posts? When he and his comments become a primary topic of conversation. Someone please post a WS drama blog in their own space and take it there. That would be nice.Addendum: I see the effect worsened as I typed this post. Apropos.

Quoting islandblow:So here I am on Dominica, Lesser Antilles, waiting to be sideswiped by Ana and maybe hit by Bill-to-be if he keeps going west. Will get high seas on the Atlantic coast of the island in any case, so fihermen are being warned to drag up their boats off the beaches.

Quoting WeatherStudent:So no longer a SF threater from either system then, Adrian? Yes, we've lucked out yet again.

Nope did not say that in anyway, model consensus has somewhat shifted to our south GFDL/HWRF etc... land interaction now looks like a pretty big issue with this small disturbance.Just watch and see what developes over the next 2-3 days.

Good evening everyone. Living here in Tampa, Florida and this is by far the best place to get up to the minute information on the tropics and I have learned a lot from all of you. Being a photographer, mother nature has a way to not only show her nasty side, but can be quite beautiful as well. While I am far from qualified to provide as much information as most of you, I can show what I am seeing here in the bay area through my viewfinder.

Last year was my first attempt and I will try to capture what it looks like if any storms pass through the area. Here is just one of the many images I captured as Ike took a glancing appearance here in the area. The image was taken on Honeymoon Island, Florida.

Thanks everyone for your valuable insight as well as to Dr. M for a great learning resource.

With every run it looks better and better for Miami and Ft. Lauderdale! Ana shifted way south and Bill is shifting away from Fl too! I don't know how we do it here in S Fla but we keep getting missed. Don't get me wrong, we need the rain but with Ana and Bill certain to miss us it is for sure a relief!

With every run it looks better and better for Miami and Ft. Lauderdale! Ana shifted way south and Bill is shifting away from Fl too! I don't know how we do it here in S Fla but we keep getting missed. Don't get me wrong, we need the rain but with Ana and Bill certain to miss us it is for sure a relief!

I have been seeing a more organized pattern develop within Bill today. The eastern band continues to wrap around the eastern side of the circulation cutting off the dry air intrusions that have been haunting the coc. More convective activity continues to occur around the circulation indicative of a more moist environment for Bill. This is also indicative of less wind shear and warmer SSTs. Ana is more on life support as her circulation is still well west of the convection. The tropical wave/LLC around Florida is going through a cycle of convection, but I expect it to redevelop as a more definitive circulation is evident on visible satellite imagery. Bill's coc is now able to develop is own more intense convection now that the atmosphere is more moist and secluded from the dry air source. I expect him to look a lot better later this afternoon and evening. Ana is fighting a lot of dry air and wind shear today. I don't expect her to look better until tomorrow.

The east and northeast side seem to be of marginal import currently as Bil is chugging westward like a bat out of hell and the west side is looking pretty damn good. I think the east side is the result of the shear but that'll stop by the beginning of the workweek, ad after that it's pretty much a straight shot to the islands with nothing around but wet, warm, dead air around the TS, no shear to speak of, and plenty of warm, deep water below it for Bill to suck up.

just calm down follow guidance from NHC listen to local officials we got a couple days before anything starts to affect people first in line are my friends in northern leewards lets keep things flowing smoothly for them